Abstract

Background

Preventing injuries among children and young people is a priority in England and worldwide; with injuries a leading cause of death, ill health and disability in children, and resulting in substantial costs to health services and society. Understanding the burden of injuries is important for health service planning and the prioritisation of preventative interventions to those at greatest risk. Despite this, estimating injury burden in England remains a challenge due to fragmented data collection systems and no national surveillance system. The recent linkage of a large primary care research database, the Clinical Practice Research Datalink (CPRD), to hospitalisation and mortality data, offers a new opportunity to study the epidemiology of injuries and provide more complete estimates of injury incidence.

Mental illnesses are the commonest morbidity women experience during pregnancy and the postnatal period, and are associated with several child health outcomes. The impact of maternal mental illnesses on the occurrence of childhood injuries is underexplored; with existing studies giving mixed findings, focusing upon depression alone and relying on maternal reporting of injury occurrences. Existing studies suggesting an association between maternal perinatal depression and childhood injuries have not considered the role of ongoing maternal depression after the postnatal period, and whether observed associations could be explained by biases in the reporting of injuries by mothers, or the recording of injuries by clinicians.

Methods

Three large routinely-collected datasets from England, the CPRD, Hospital Episode Statistics (HES), and Office for National Statistics (ONS) mortality data, were used to conduct a series of studies.

1. The epidemiology of injuries among children and young people. A cohort of 1,928,681 individuals aged 0-24 years old from England who had linked CPRD, HES and ONS mortality data was used to describe the epidemiology of three common injuries (poisonings, fractures, burns). Time-based algorithms were developed to identify incident injury events, distinguishing between repeat records for the same injury, and those for a new event. Injury incidence rates and adjusted incidence rate ratios (aIRR) were estimated by age, sex, calendar year and socioeconomic deprivation. The recording of injury mechanisms and intent were examined for the three data sources.

2. Maternal mental illnesses during pregnancy and the child’s first five years of life. A cohort of 207,048 mother-child pairs from England who had linked CPRD and HES data, with children born 1998-2013, was used to define episodes of maternal depression and/or anxiety (termed ‘depression/anxiety’) using diagnostic, prescription and hospitalisation records. Incidence rates of maternal depression/anxiety were described over the child’s first five years of life.

3. Maternal perinatal depression and injuries in children aged 0-4 years old. A cohort study of 207,048 mother-child pairs compared incidence rates and adjusted incidence rate ratios of child poisonings, fractures, and burns among children whose mothers had experienced perinatal depression with those who had not. To assess how the association between perinatal depression and child injury was affected by subsequent exposure to maternal depression, adjusted incidence rate ratios were compared for mothers whose depression continued beyond or recurred after the postnatal period, with mothers in whom it did not. Analyses were repeated for a group of serious injuries where injury ascertainment was more likely to be complete.

4. Association between episodes of maternal depression/anxiety and rates of child injuries. Two analyses, a traditional cohort analysis (a between person design) and a self-controlled case series (SCCS) analysis (a within person design where individuals act as their own controls), were used to compare incidence rates of child injuries during episodes of maternal depression/anxiety with periods when mothers had no evidence of depression/anxiety in their medical record. These two methods were compared as they account for confounding by different means.

Results

1. The epidemiology of injuries among children and young people. For the period 2001-2011, incidence rates of poisonings, fractures and burns were 41.9 per 10,000 person-years (PY) (95%CI 41.3-42.5), 185.5 (95%CI 184.6-186.4) and 34.6 (95%CI 34.2-35.0), respectively among the cohort of 0-24 year olds. Of the injury events identified in linked CPRD-HES-ONS mortality data, 18,065 (51%) poisonings, 117,102 (75%) fractures, and 26,276 (91%) burns were only recorded in primary care data (CPRD). Injury mechanism and intent recording was high within hospitalisation and mortality data (80-100%), but low in primary care data (2-4% of burns and fractures).

Age patterns of injury incidence varied by injury type, with peaks at age 2 (69.4/10,000 PY) and 18 (76.0/10,000 PY) for poisonings, age 13 for fractures (310.1/10,000 PY) and age 1 for burns (113.1/10,000 PY). Over time, fracture incidence rates increased, whereas poisoning rates increased only among 15-24 year olds and burns incidence reduced. Poisoning and burn incidence rates increased with deprivation, with the steepest socioeconomic gradient between most and least deprived quintiles for poisonings (aIRR 2.20, 95%CI 2.07-2.34).

2. Maternal mental illnesses during pregnancy and the child’s first five years of life. 4,210 (2.0%) mothers had antenatal depression, 20,486 (9.9%) had postnatal depression, and 7,413 (3.6%) had both. Between the child’s birth and fifth birthday, 54,702 (26.4%) children were exposed to one or more episode of maternal depression/anxiety, with incidence rates of maternal depression, depression with anxiety and anxiety alone 6.92/100 PY (95%CI 6.86-6.98), 1.30 (95%CI 1.27-1.33) and 1.83 (95%CI 1.80-1.86), respectively.

3. Maternal perinatal depression and injuries in children aged 0-4 years old. Among 207,048 children, 2,614 poisonings, 6,088 fractures and 4,201 burns occurred during follow-up. Children whose mothers had perinatal depression had higher injury rates than children who were unexposed, with associations strongest for poisonings. Compared to those unexposed, poisoning rates were 74% higher among children exposed to antenatal depression (aIRR 1.74, 95%CI 1.39-2.18), 55% higher for postnatal depression (aIRR 1.55, 95%CI 1.39-1.72) and 89% higher for children exposed to both (aIRR 1.89, 95%CI 1.61-2.23). Children also exposed to maternal depression when aged 1-4 years old tended to have higher poisoning, fracture and burn rates than children only exposed to perinatal depression. Significant associations persisted when analyses were restricted to serious fractures and burns.

The study populations for the SCCS analyses consisted of 2,502, 5,836, 4,051 and 909 children who had experienced a poisoning, fracture, burn or serious injury, respectively. For children who experienced a poisoning or burn, poisoning (aIRR 1.48, 95%CI 1.19-1.85) and burn (aIRR 1.29, 95%CI 1.07-1.55) rates were only increased during periods when the mother had depression compared to periods when the mother had no evidence of depression/anxiety in their medical record. No significant differences in fracture or serious injury rates were seen during depression/anxiety episodes compared to unexposed periods.

Conclusion and implications

It is essential to use linked primary care, hospitalisation and mortality data to estimate injury burden, as many injury events are only captured within a single data source. Linked routinely-collected data may offer an affordable mechanism for injury surveillance; although is limited by poor recording of injury mechanism and intent within primary care data. Differing injury patterns according to age and injury type reflect differences in underlying injury mechanisms, highlighting the importance of tailored preventative interventions across the life course. Inequalities in injury occurrences support the targeting of preventative interventions to those living in the most deprived areas. Future work includes extending this research to other injury types and incorporating emergency department data when this becomes available.

Approximately 1 in 4 children were exposed to maternal depression/anxiety between birth and their fifth birthday, highlighting maternal depression/anxiety as a common exposure of childhood. The studies presented in this thesis suggest maternal depression is a modifiable risk factor for childhood injuries. The consistent finding of higher poisoning and burn rates during maternal depression episodes, in both the traditional cohort and SCCS analyses, mean associations are unlikely to be fully explained by residual confounding. The lack of association between maternal depression with anxiety episodes and child injuries in the SCCS analysis may relate to confounding variables being controlled for in the SCCS analysis that could not be controlled for in the traditional cohort analysis, but may also relate to study power and the chronicity of depression with anxiety episodes.

The significant associations between perinatal depression and child injuries highlights the importance of screening mothers for perinatal depression and ensuring they receive appropriate treatment and support. Clinicians working with young families, such as general practitioners and health visitors need to be aware of the increased injury rates among children of depressed mothers. These clinicians can refer families to support groups (e.g. parenting groups), for home safety advice and to equipment schemes where these are available. In addition, pharmacists and prescribers should consider providing advice about safe medication storage and disposal to mothers being managed for depression/anxiety. Future research could include; qualitative studies exploring mothers’ perceptions on child injury prevention, managing a mental illness and the support they would find beneficial, and work to assess associations between serious mental illnesses (e.g. schizophrenia and bipolar disorder) and child injuries.